Release from underground storage tanks (UST) is one of the most common contamination sources. Most of the Nonaqueous Phase Liquids (NAPLs), which are the main content of an UST release, are restricted by law and regulation to a very low concentration in drinking water due to its hazardous nature. Even a very small amount of NAPLs in the groundwater can pose a serious risk to the environment. For example, one gallon of gasoline, which contains about two percent benzene, can contaminate up to one million gallons of groundwater over the drinking water standard. Remediation of such contamination is very costly, time consuming and, worst of all, very inefficient in most of cases. Considering the number of USTs throughout the world, the millions of dollars spent every year to deal with UST contamination is not sufficient to deal with every UST.
For various reasons, it is very difficult to make an underground storage tank completely free from release. For over 20 years, various regulations have been imposed on the manufacture and installation of USTs. However, it has been found that the release from USTs still contaminates groundwater and surrounding aquifer formations, even if the UST meets all of the requirements set forth in regulations and passes all of the accompanying test. Under these circumstances, it is better to shift the focus from preventing an UST from leaking to keeping any possible leakage from contaminating groundwater and surrounding geological formations.